LED-based emergency lighting equipment and methodology
View Patent ↗Systems and methods provide LED-based emergency lighting utilizing AC-DC switch mode power conversion technology, NiMH battery technology, and emergency lighting lamps that use high power white LEDs as the emergency lighting source. A low voltage microprocessor based circuit design reduces the battery input voltage for the unit to a nominal level of 2.4 VDC. The microprocessor executes a pulse charging algorithm to lower battery maintenance mode power consumption levels and extend the useful life of the battery. Brownout detection technology does not require the determination of the AC input voltage level or transmission of the brownout detection signal to the secondary side of the circuit. A rechargeable battery is charged by a charge current selectively set to a bulk charge value, a trickle charge high value, or a trickle charge low value based on sampling of the voltage of the rechargeable battery and the charge current.
1. A method for charging a rechargeable battery by a charge current comprising the steps of
(a) sampling a voltage of said rechargeable battery and said charge current;
(b) if said voltage of said rechargeable battery is less than or equal to a voltage threshold value and said charge current is less than or equal to a current threshold value, setting said charge current to a bulk charge value and applying said charge current to said rechargeable battery for a bulk charge time period;
(c) if said voltage of said rechargeable battery is greater than or equal to a low voltage threshold value and less than or equal to said voltage threshold value and said charge current is within a certain range of said bulk charge value, and a duration of said bulk charge time period is greater than or equal to a bulk charge time expiration period, setting said charge current to a trickle charge low value and applying said charge current to said rechargeable battery for a trickle charge low time period;
(d) if said charge current is less than or equal to a current threshold value, and a duration of said trickle charge low time period is greater than or equal to a trickle charge low time expiration period, setting said charge current to a trickle charge high value and applying said charge current to said rechargeable battery for a trickle charge high time period;
(e) if said voltage of said rechargeable battery is greater than or equal to said low voltage threshold value and less than or equal to said voltage threshold value and said charge current is within a certain range of said trickle charge high value, and a duration of said trickle charge high time period is greater than or equal to a trickle charge high time expiration period, setting said charge current to a trickle charge low value and applying said charge current to said rechargeable battery; and
(f) repeating said steps (a) through (e) at least once.
2. The method of claim 1 , wherein said voltage threshold value is proportional to a number of cells of said rechargeable battery.
3. The method of claim 1 , wherein said certain range of said bulk charge value is within about +/−10% of said bulk charge value.
4. The method of claim 1 , wherein said certain range of said trickle charge high value is within about +/−10% of said trickle charge high value.
5. The method of claim 2 , wherein said voltage threshold value is about 1.65V multiplied by N, where N is equal to a number of cells of said rechargeable battery.
6. A method for charging a rechargeable battery by a charge current comprising the steps of
(a) sampling a voltage of said rechargeable battery and said charge current;
(b) if said voltage of said rechargeable battery is less than or equal to a voltage threshold value and said charge current is less than or equal to a current threshold value, setting said charge current to a bulk charge value and applying said charge current to said rechargeable battery for a bulk charge time period;
(c) calculating a delta V/delta t value of said voltage, wherein V is said voltage of said rechargeable battery, and t is time;
(d) if said delta V/delta t value is less than or equal to about zero for a first conditional time period, or if during a second conditional time period said delta V/delta t value is not less than or equal to about zero for said first conditional time period, setting said charge current to a trickle charge low value and applying said charge current to said rechargeable battery for a trickle charge low time period;
(e) if said current of said charger circuit is less than or equal to said current threshold value, checking at trickle charge low check time intervals a duration of said trickle charge low state, and if said duration of said trickle charge low state is greater than or equal to a trickle charge low time expiration period, setting said charge current to a trickle charge high value and applying said charge current to said rechargeable battery for a trickle charge high time period; and
(f) repeating said steps (a) through (e) at least once.